The present invention relates generally to a method and apparatus for cooling a gas turbine and relates more particularly to a method and apparatus for cooling a turbine of an air-storage system, the turbine having at least one turbine stage which includes an axial flow-through of hot propellant gas.
An accumulation of heat will usually take place in gas turbines of an air-storage system after the turbine has been shut-off. This accumulation of heat is caused by the windage work performed during the deceleration of the machine as a result of contact of the machine blades with air. The accumulation of heat can result in an unduly sharp rise in the temperature of the turbine components.
Accordingly, an object of the present invention is to eliminate, or to at least maintain within a safe magnitude, any rise in temperature caused by the windage work.
According to the present invention, in a gas turbine having at least one turbine stage with axial flow-through, a gaseous medium of lower temperature, especially air, is conveyed to the turbine stage, or at least one turbine stage if several stages are involved, following a cut-off of the propellent gas flow. The blading of the turbine which operates as a ventilator during the deceleration of the turbine, compresses the gaseous medium being conveyed to the stage, with the gaseous medium continuing its flow to an exhaust gate of the turbine. Since the temperature of the gaseous medium being conveyed is preferably equal to the ambient temperature and is lower than the temperature of the propellant gas during the operation of the turbine, the gaseous medium will be able to absorb the windage heat without undergoing an undue rise in temperature. The turbine may even be cooled-off by a proper selection of the temperature level of the gaseous medium being conveyed. It will be necessary, however, to provide a volume of gaseous medium that is sufficient to dissipate the resultant amount of windage heat without resulting in an undue increase in temperature of the gaseous medium.
When viewed in the direction of flow, the blade rings of a turbine stage which are last have the greatest diameter, and, thus, perform a greater percentage of the windage work. Accordingly, it will be sufficient in many instances and also advantageous to convey the gaseous medium to one of the last blade rings of at least one turbine stage. Furthermore, if the turbine has several turbine stages it will be expedient to convey the medium at least to the last turbine stage.
The medium can be conveyed to the desired turbine stage or stages most advantageously if the corresponding combustion chamber is provided with an intake for the gaseous medium which can be shut off. In this manner, the gaseous medium is conveyed by way of the combustion chamber of the specific turbine stage, with the result that the gaseous medium initially provides a cooling for the combustion chamber and that the medium undergoes some pre-heating to thereby avoid a sudden and sharp cooling of the turbine blading.
In a more preferred form of the present invention, an annular duct surrounds the blade ring and is provided with apertures leading to the blade ring. The gaseous medium is supplied to the annular duct through an intake for the medium that can be shut off. This addition of the annular duct does not require a costly outlay to be made.
The medium can be conveyed to the intakes or connecting points by a compressor or by a ventilator. In a gas turbine which is used in connection with an air-storage system, however, it will be expedient to connect the intakes directly with the air-storage compartment.